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Title: TEMPERATURE DEPENDENT DIELECTRIC PROPERTIES OF SUBTROPICAL AND TROPICAL FRUITS AND INSECTS

Author
item WANG, SHAOJIN
item MONZON, MARIA
item GAZIT, YAOV
item TANG, JUMING
item MITCHAM, ELIZABETH
item Armstrong, John

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2005
Publication Date: 8/1/2005
Citation: Wang, S., Monzon, M., Gazit, Y., Tang, J., Mitcham, E., Armstrong, J.W. 2005. Temperature dependent dielectric properties of subtropical and tropical fruits and insects. Transactions of the ASAE. Vol. 48(5): 1873-1881.

Interpretive Summary: Knowledge of the dielectric properties of commodities and insect pests is important in developing thermal treatments for postharvest insect control based on radio frequency (RF) and microwave energy. To add to the literature regarding dielectric properties of tropical and subtropical fruits and their corresponding pests, the dielectric properties of Mediterranean fruit fly, Mexican fruit fly, oriental fruit fly and melon fly and of avocado, cherimoya, longan, passion, persimmon, and white sapote were measured and subjected to 1-1800 MHz frequency and 20-60°C to determine how these treatment parameters affected these properties. Additionally, the penetration depth of 27, 915 and 1800 MHz into these fruits were measured, along with the matching saline solutions to have uniform heating when subjected to RF systems based on the electrical conductivity. This information adds to the literature new parameters for dielectric properties and the affects of treatment parameters for scientists developing heat disinfestation quarantine treatments, especially those using radio frequency and microwave energy treatments.

Technical Abstract: The dielectric properties of six tropical fruits along with four associated insect pests were measured between 1 MHz and 1800 MHz using an open-ended coaxial-line probe technique and at temperatures between 20 and 60°C. The dielectric loss factor of the tropical fruits and insects decreased with increasing frequency at constant temperatures. Especially over 10 to 300 MHz, the log of the dielectric loss factor decreased linearly with the log of increasing frequency. The loss factor of the fruits and the insects increased almost linearly with increasing temperature at 27 MHz radio frequency, but remained in a small range at 915 MHz microwave frequency. Both the dielectric constant and the loss factor were the highest in avocado fruit, especially at 27 MHz. Similar dielectric loss factors for insects and tropical fruits suggested that differential heating was unlikely to occur in RF and microwave systems. Direct measurement of electrical conductivity of fruit pulps made a good estimation of the dielectric loss factor at 27 MHz and a matched saline solution based on electric conductivity might be used to improve heating uniformity of tropical fruits when subjected to RF systems.